1. Field of the Invention
The present invention relates to the field of electrocardiogram analysis.
2. Description of the Related Art
For over a hundred years since the invention of the electrocardiograph which produces a graphical recording (i.e. an electrocardiogram (ECG) which may be recorded on paper or stored as electronic data) of electrical activity of a heart over time. In the prior art there are two main perspectives in the study of the heart's electrical signals: (1) morphology, the meaning of the different deflections that appear to repeat from beat to beat, and (2) rhythm (or arrhythmology as used herein), the meaning of the different periodicities of these signals. Morphology is the study of electrocardiograms and is focused on the detection of muscular or conductional abnormalities within a beat such as myocardial ischemia, hypertrophies, bundle branch blocks, and the like. Arrhythmology is the study of electrical firing and conduction abnormalities such as ventricular premature beats, conduction blocks, and the like. An electrocardiogram as used herein may be a recording of a part of one (heart) beat, a complete beat, or more than one beat.
Myocardial ischemia is traditionally detected by morphological analysis, where an abnormally elevated or depressed deflection of the ST-segment within each beat indicates possible ischemia. Prior art methods of electrocardiogram analysis and interpretation, mainly visual inspection of the time-domain electrocardiogram, provide a poor expectation of about 30 to 60% accuracy in detection of ischemia.
Other methods of ischemia detection include pattern recognition methods such as frequency-domain analysis and wavelet-transform analysis. Pattern recognition involves taking a resource-limited observation (RLO) and a resource-rich observation (RRO) from the same subject. An RLO is an observation that is non-invasive, inexpensive, and time-efficient such as a conventional ECG. An RRO is an observation that is more invasive, more expensive, and less time-efficient as compared to an RLO such as exercise electrocardiography, dobutamine stress echocardiography, single positron emission computerized tomography (SPECT) Thallium-201 scanning, coronary angiography, and the like. RRO observations are more accurate in detecting ischemia as compared with conventional standard resting electrocardiogram analysis.
One pattern recognition method for detecting ischemia employs energy spectral density (ESD) analysis (sometimes referred to as power spectral density (PSD) analysis) of the harmonics of an electrocardiogram. See e.g. Fang & Hone, Principle and clinical application of Bio-Cybernetic Cardio-Diagnostic System (BKD) C2001; Fisher (1998) Biomedical Instrumentation Technology, 32(4):387; Noera & Oueida (1999) Giornale della Arteriosclerosi 34(2):81; and U.S. Pat. Nos. 5,649,544, 6,638,232, and 6,148,228; Fokapu & Girard (1991) Electrocardiography 12(2):645; Jones et al. (1992) J Electrocardiograph 25(Suppl):188; Rozentryt et al. (1999) Med Sci Monit 5(4):777; Haberl et al. (1989) European Heart J 10:316; Sierra et al. (1997) Proc 19th Int'l Conf IEEE/EMBS p. 76. Unfortunately, ESD methods and analysis are difficult to interpret and correlate to morphology consistently.
Therefore, a need still exists for methods, systems and devices for detecting and diagnosing heart diseases and disorders such as ischemia.